The present invention relates to a unique knock-down framework joint which offers limitless arrangements for storage and display racks, exhibit booths, and the like, for department store merchandizing, office, laboratory, institutional and do-it-yourself home applications.
Various knock-down framework arrangements have been heretofore developed which utilize a connector joint or fitting to interconnect square tubes which fitting has a cubical hub from which outwardly extends from two or more faces thereof tube-receiving projections or posts. Each of the tube-receiving projections on initial assembly with a tube fits loosely within an open end of the tube in one angular position of insertion thereof, and tightly frictionally engages the inner defining walls of the tube when the tube or fitting is rotated 45.degree. from its initial position. Examples of such know-down frameworks are disclosed, for example, in U.S. Pat. No. 3,532,369, granted Oct. 6, 1970, and British Pat. No. 1,011,688, granted Dec. 1, 1965. To prevent the withdrawal of the interconnected parts from their supposed tightly fitting positions by a force tending to separate the parts longitudinally, a locking tongue is sometimes provided on each end of the tube which tongue fits into a groove formed in the associated tube-receiving projection. However, this licking tongue heretofore served the sole purpose of preventing the separation of the parts in a longitudinal direction.
In the commercial forms of the knock-down frameworks shown in the patents described, at least one or both of the inter-fitting surfaces, generally the outermost surfaces of the tube-receiving projections of the connector fitting, are made of a synthetic plastic material. Such a plastic material is subject to wear and dimensional instability which affects adversely the reliability thereof over long periods of use. Also the tolerances utilized in the manufacture of the connector fittings and the square tubes were such that the telescoping parts thereof sometimes did not fit tightly together as desired, resulting in a weak or wobbly framework.
Another deficiency of the prior art knock-down frameworks of the type described is that frequently the ends of the square tubes did not fit snugly and neatly against the faces of the cubical hubs of the connector fittings, leaving unsightly openings thereat.
It is, accordingly, one of the objects of the invention to provide an improved knock-down framework joint of the general type described above which, when the telescoping tube-receiving projections of the connector fittings and the square tubes are in their tightly fitting positions, they will always fit snugly together even when made with only modestly stringent manufacturing tolerances.
A further object of the invention is to provide a knock-down framework joint of the type described wherein the relative rotation of the initially loosely fitting telescoping parts into a joint locking position automatically draws the square tube involved snugly against the face of the cubical hub of the connector fitting, so that no unsightly gaps are visible between the tube and the connector fitting.
A still further object of the invention is to provide a knock-down framework joint as described wherein the parts thereof, even after repeated assembly and dis-assembly thereof, continue to form a secure, tightly fitting joint.